The paper is conventionally formed from a suspension of about 0.4% to 1.2% fiber solids (fibers) through a so called head box by spreading the suspension on a moving rotating wire, or a nip, formed by two rotating wires, followed by removing the suspension water as much as possible in consequent process steps through vacuum, pressing and drying.
During paper web forming process or immediately thereafter, web interior and surfaces will require treatments to bring paper properties to acceptable level. These properties include printability, rigidity, strength and chemical penetration that are achieved through chemical treatment, filling and coating materials, and mechanical doctoring processes, some of which are specific for different paper and board grades.
To increase paper whiteness and paper printing properties, the first approach is to add fillers, such as kaolin, and mix them together with around 1% fiber solution to reach filler contents typically from 5% to 35% in the final paper or board. However, up to 40% of these fillers go through the forming paper web on a moving wire, ending into recirculation.
The so called ply-bond between two paper layers is currently achieved by excessive refining of the fibers or by spraying a dilute 2% starch on wire section between the layers. The low solids content is currently needed to minimize aerosol formation and nozzle plugging.
Paper surface strength and rigidity are accomplished by surface sizing during the paper drying process. The size is typically added by immersing the sheet into the size solution at around 8% solids, or by applying size films with a two roller nip on dry paper sheet surfaces at 8% to 10% consistency. The low consistency causes considerable amount of paper rewetting requiring re-drying. The sheet must be fully dry at the application points as it can not otherwise withstand the mechanical forces around these processes.
Paper is coated by adding up to 90% excess coating solution on the paper side and doctoring the excess solution to recirculation system. The coating solutions have typically high viscosity with solids from about 45% to 65%. The paper must be fully dry before first coating is applied and must also be dried between the consequent coating solution applications. Wet paper can not withstand the mechanical forces that are higher than with sizing. In this process the coating solution, often at zero initial machine speed, hits the paper web moving at speed up to 1800 meters per minute, accelerates to this speed, and comes to a full stop when up to 90% excess is doctored away for the desired coat weight on the paper or board surface.
Most of the paper grades are re-moisturized during the drying process to correct for the continuously changing CD moisture profile resulting from the shifting imbalances in the dryer section and slowly changing mechanical conditions on the machine.
The existing paper making, filling, sizing and coating methods lack the ability to apply a precise amount of material on the sheet to a specific position and can not as such provide means for cross directional (CD) profiling. Among these the paper making process itself has had a best CD profiling capability through a somewhat flexible metal lip opening in the so called Head Box that distributes the flow on a moving wire or wire nip. The lip opening is narrowed or widened through automated mechanical screws or thermally expanding metal bars. Unfortunately the total dynamics of this process at around 1% solids is difficult to master as every move has an impact elsewhere around it. Industry developed several computer algorithms to master the process but this was not enough. The next step was a so called dilution Head Box, where the individual Head Box sections are diluted with r circulating water to achieve the desired material amount to a specific position. This was a major improvement for the industry but it still lacks the ability to fully control the process especially against the still shifting fiber orientation that will at the end impair the product quality.
This invention of paper fiber spraying allows complete control over the fiber orientation at any position, and additionally it allows a precise spray layer based engineering of the paper sheet in such a way that none of the current methods can do and provides the first time the ability to make fully engineered paper utilizing the variety of raw materials maximally.
The use of original spraying technology for paper re-moisturizing turned to a huge success with advancement of computer technology in the early 70's. Spraying of other materials has periodically been tested e.g. for paper surfacing but the results were largely unsuccessful. Even the latest applicator methods as presented in the U.S. Pat. No. 4,944,960 with improvements shown in the European Patent EP 0682571 still lack their first commercial application. The paper manufacturing itself has also been tried with gap sprayer technology but so far without success. One of the key components for fiber spraying is the nozzle shown in the recent U.S. Pat. No. 6,866,207 by Kangas.
For spraying the nozzle must be energy efficient, the spraying direction must essentially be downwards with gravity when other liquids than water are sprayed, the aerosols must be controlled, the spray pattern must be stable at varying nozzle flow rates for CD profiling, and in some cases the spray fog that has attached onto the substrate has to be doctored with a specific doctoring device according to this invention. The systems are illustrated in FIGS. 12, 13, 14 and 15.
The benefits of this invention can be summarized as follows:                All paper and board filling, sizing, coating, and barrier surfacing can be accomplished in a simple and efficient way using this spraying process.        All paper and board grades can be manufactured using this spraying process leading to sizeable savings in the energy consumption of their manufacturing.        Paper and board can now be engineered through spray-layer approach according to this invention.        The system poses no limitations to the paper machine operating speed and is a major improvement in paper machine operating efficiency and productivity.        Lower strength and other raw materials can be utilized more efficiently throughout the paper making process.        The aerosol release to work environment is eliminated. Aerosols are formed whenever material is sprayed in room air environment and in film splitting typically found in size presses and similar paper pigmenting process.        